用耦合功率理论分析缺陷双包层光纤吸收效率

Study on the Absorption Efficiency of Truncated Double-clad Fiber with Coupled Power Theory

当泵浦光在内包层有缺陷的双包层光纤(DCF)内传输时,只有在光纤中心处有场强的LP0n模才能直接被单模掺杂纤芯吸收;但根据耦合模扩散理论,与LP0n模对应的一组亮环最邻近的2n个亮环所携带的功率能耦合进LP0n模,被纤芯吸收。运用耦合功率理论中的功率耦合系数方程,算得2n个亮环与相应LP0n模间的2n个功率耦合系数,将之相加得到总的功率耦合系数。根据此系数的大小,可以判断单位长度内掺杂纤芯吸收光功率能力的强弱。运用这种方法计算内包层为D型、有双重缺陷和矩形的DCF的功率耦合系数,可以发现,在内包层缺陷面积相等的前提下,前者的吸收效率更大,这结果用基于射线法的等亮度定理是得不到的。

While the pumping light is transmitting in double-clad fiber (DCF) with truncated inner cladding, only the LP0n modes having electric intensity in the center of DCF can be absorbed directly by the RE-doped core. But according to coupled modes diffusion theory, 2n bright loops that are adjacent to the n bright loops corresponding LP0n modes will couple into LP0n modes, then be absorbed. Using the power coupling coefficient equations of coupled power theory, the total power coupling coefficient between the 2n bright loops and corresponding LP0n modes was obtained. Then the intensity of the absorption efficiency of DCF in per length was estimated according to this coefficient. The power coupling coefficients of D-shaped, double-truncated and rectangular DCF were calculated by this method. It could be found that the absorption efficiency of the D-shaped DCF is stronger than others if the truncated areas in inner cladding of these DCF's are equal. The result can't be obtained by the brightness theorem based on ray theory.